1. Field of the Invention
The present invention relates to a resin-sealed surface mount electronic device.
2. Description of the Prior Art
With reductions in the size of electronic equipment, there has been an increase in the use of surface mount semiconductor devices, such as diodes and transistors, and the size of these devices also is being reduced.
FIG. 3 shows the general construction of a surface mount diode of the past, FIG. 3(A) being a plan view thereof, and FIG. 3(B) being a cross-section view as seen from the direction indicated by the arrows along the line IIxe2x80x94II in FIG. 3(A).
The electronic device 100 of FIG. 3 has a first external lead 110, which has a electronic element placement pad (die pad) 111 for placement of an electronic element, and a second external lead 120, which is disposed at a distance from the element placement pad 111. A semiconductor element 130 is placed on the element placement pad 111. A bonding wire 150 makes a connection between an external connection terminal of the semiconductor element 130 and the second external lead 120. The semiconductor element 130, the electronic element placement pad 111, the inner lead part of the first external lead 110, the inner lead part of the second external lead 120, and the bonding wire 150 are sealed by a sealing resin 140. As shown in this drawing, the first external lead 110 and the second external lead 120 are bent in an S shape, with one end of the leads 110 and 120 exposed to the outside of the sealing resin 140, so as to form outer lead parts. The lower surfaces of the outer leads extend in a direction that is substantially parallel to the bottom surface 141 of the sealing resin 140, and are substantially on the same plane as the bottom surface 141 of the sealing resin 140.
The above-noted electronic device is manufactured by first punching out and bending a thin metal sheet to the appropriate shape to form a lead frame, onto which the semiconductor device is placed. Then, after making the prescribed connections, the device is sealed using sealing resin. The sealing with the sealing resin 140 is done within a die of the prescribed shape, so as to include the electronic element placement pad 111, the inner lead part of the first external lead 110, and the inner lead part of the second external lead 120, resin being injected via a resin injection port 190, indicated by the double-dot-dash line, on one of the shorter sides of the device.
The dimensions of a usual resin sealed electronic device of the past were approximately a vertical dimension (X-axis dimension LX in FIG. 3) of 1.3 mm, a horizontal dimension (Y-axis dimension LY in FIG. 3) of 0.8 mm, and a height (Z-axis dimension H in FIG. 3) of 0.7 mm.
Because the thickness of the lead frame used in an electronic device of the past was 0.1 mm or greater, however, it was difficult to achieve a surface mount electronic device with a resin package having all of the vertical, horizontal, and height dimensions smaller than approximately 1 mm, including resin-sealed semiconductor devices making use of a semiconductor substrate.
Because the thickness of the lead frame is 0.1 mm or greater, the spacing between the element placement pad 111 of the first external lead 110 and the second external lead 120 grows to over 0.2 mm by the formation of the lead. Because of the relationship between such parameters as the lead bending depth, the associated thickness of the resin at the bottom of the element placement pad 111 that is required therefor, the lead length required for bending, and the establishment of a flat surface for placement of an element, in the case of diodes in particular, it was not possible to achieve a vertical length of less than 1.0 mm.
As electronic devices became smaller, because of the delicate bending shape of the bent parts 112 and 122 near the bottom surface of the sealing resin of the external leads, there was a tendency toward such problems as insufficiencies in the adhesion and filling in of sealing resin, the strength of the lead itself, and the adhesive strength between the lead and the sealing resin, and poor adhesion and filling in of solder used for mounting, and it was difficult to achieve an electronic component that provided improvements in these deficiencies.
Accordingly, it is an object of the present invention to provide an electronic device that solves the problems of the limitation in size reduction of surface mount resin sealed electronic devices in the past, and to enable the achievement of an electronic device having a resin package with vertical, horizontal, and height dimensions that are all below 1 mm.
It is another object of the present invention to provide a resin sealed surface mount electronic device that, even with a reduction in size of the electronic device, provides good filling in of sealing resin to the bent parts near the bottom surface of the sealing resin of the external leads, good adhesion strength between the leads and the sealing resin, and good strength in the leads themselves, and further providing good adhesion and filling in of solder when the device is mounted.
To achieve the above-noted object, the present invention has the following constitution.
Specifically, a first aspect of an electronic device according to the present invention has an electronic element, a first external lead with an element placement pad having a thickness t of less than 0.1 mm, and a second external lead that is disposed at a distance from the above-noted element placement pad, wherein the electronic element, the element placement pad, part of the first external lead, and part of the second external lead are sealed with a sealing resin, the first external lead being bent in an S shape, the bending depth d thereof being at least as large as the thickness t of the first external lead, and the thickness T of the resin on the non-device side of the element placement pad being smaller than the bending depth d.
In the first aspect of an electronic device of the present invention, the first external lead thickness t, the relationship of this thickness t to the bending depth d, and the relationship between the sealing resin thickness T at the bottom of the element placement pad and the bending depth d are established. By doing this, it is possible to limit the height of the electronic device, and to achieve the flat area required in the element placement pad. Additionally, because the spacing between the element placement pad and the second external lead can be made short, it is possible to reduce the dimension in the vertical direction.
In the configuration of the above-noted first aspect of the present invention, it is preferable that the spacing between the element placement pad and the second external lead be made no greater than 0.12 mm. Using this preferable configuration, it is possible to make a further reduction in the vertical-direction dimension of the electronic device.
In the above-noted configuration, it is preferable that the outer vertical, horizontal, and height dimensions of the sealing resin all be no greater than 1.0 mm. Using this preferable configuration, it is possible to achieve a compact electronic device that was not possible to achieve in the past, thereby contributing to the reduction in size of electronic equipment.
In the first aspect of the present invention, it is preferable that the width of the inner lead parts of the first and second external leads within the sealing resin be of a substantially uniform width and not broaden beyond the exposed part. Using this preferable configuration, it is possible to obtain a compact electronic device having a width (Y-direction dimension) that does not become large. The effect of reducing the package size is particularly significant in the case in of an electronic device having three or more terminals.
In the above-noted configuration, it is preferable that the thickness of the electronic element be substantially the same as the thickness t of the first external lead. Using this preferable configuration, it is possible to make the height of the bonding wire the same as that of the chip.
In the above-noted first aspect of the present invention, it is preferable that the sealing resin be injected from a position on either of the longer sides that is offset towards a shorter side. By providing a sealing resin injection port at such a position, the injected resin extends well into the package die, without a tendency toward the formation of eddies and/or accumulations, thereby preventing problems with insufficient sealing resin filling.
In the first aspect of the present invention, it is preferable that the bending radius R of outer surface of the bent part of the first external lead in the region of the sealing resin bottom surface be at least 0.05 mm, but no greater than the lead thickness t. Using this preferable configuration, it is possible not only to prevent both constriction of material and lead bending during lead formation, but also to achieve flexibility of the frame with respect to stress that is applied in downstream processes.
In the first aspect of the present invention, it is preferable that the sealing resin includes filler that has a particle diameter that is no greater than half the bending depth d of the lead. This preferred configuration facilitates the filling in of sealing resin and filler at the lower surface of the bent lead, thereby maintaining sufficient formation strength.
The second aspect of an electronic device according to the present invention has an electronic element, a first external lead with an element placement pad having a thickness t of less than 0.1 mm, and a second external lead that is disposed at a distance from the above-noted element placement pad, wherein the electronic element, the element placement pad, part of the first external lead, and part of the second external lead are sealed with a sealing resin, the first external lead and second external lead being bent at the bottom surface of the sealing resin, extending in a direction that is substantially parallel to the bottom surface of the sealing resin and being exposed. A depression is formed in the bottom surface part of the bent part of the first external lead and the second external lead, at which depression the thickness of the lead is reduced, the bottom surfaces of the depressions of the first and second external leads and the bottom surface of the sealing resin being formed so as to be higher than the lowermost surfaces of the parts of the first and second external leads which extend outside.
According to the above-noted second aspect of the present invention, by providing a depression in the bottom surfaces of the bent parts of the first and second external leads, good filling of sealing resin is achieved in the region of the bent parts, thereby improving the adhesion strength between the leads and the sealing resin, another effect being an improvement in the strength of the leads themselves. Because the bottom surfaces of the depressions and the bottom surface of the sealing resin are formed so as to be higher than the lowermost surfaces of the parts of the first and second external leads which extend outside, good adhesion and filling of solder is achieved when mounting the device to a circuit board.
In the second aspect of the present invention, it is preferable that the depression be formed within the projected boundaries of the sealing resin as seen from above. By adopting this preferred configuration, the design of the shape in the region of the depression of the resin die used for resin sealing is facilitated, and it is easy to prevent leakage of sealing resin from the area surrounding the depression when resin sealing is done. Additionally, because the formation of the depression is accompanied by a reduction in the thickness of the lead, by forming the depression within the above-noted region, it is possible to compensate for the loss of strength caused by this accompanying reduction in lead thickness by means of sealing resin in the surrounding area. Additionally, because it is possible to form the lowermost surfaces of the first and second external leads within the region that is projected from above the sealing resin, it is possible to achieve a sufficient contact surface area between the circuit board and the leads, even if the exposed parts of the first and second external leads are shortened. It is therefore possible to reduce the mounting surface area of the electronic component, thereby contributing to a reduction in size of the overall electrical equipment.
In the second aspect of the present invention, it is preferable that a sealing resin escape part be formed at the side bottom part of the sealing resin, and that bottom edge position of this escape part be substantially the same as the forming position of the depression, and that the distances between these positions and the border with the above-noted region projected from above the sealing resin both be no greater than the thickness of the lead. By forming a sealing resin escape part at the at the bottom side part of the sealing resin, removal from the resin die after resin sealing is facilitated. By making the formation position of the depression substantially the same as the bottom edge position of the escape part, it is possible to form the lowermost surfaces of the first and second external leads within a region projected from above the sealing resin. As a result, even if the parts of the first and second external leads that are exposed from the sealing resin are made short, it is possible to achieve a sufficient contact surface area between the circuit board and the leads. This enables a reduction in the size of the mounting surface area of the electronic component, therefore contributing to the reduction in size of the electronic equipment. Additionally, because the distances from the border of the region projected from above the sealing resin to the bottom edge position of the escape part and the formation position of the depression are both no greater than the lead thickness, it is possible to optimize the reduction in the device size, the lead bending angle, and the sealing resin thickness at the bottom of the element placement pad, while achieving a sufficient element placement pad.
In the second aspect of the present invention, it is preferable that the lower surfaces of the first and second external leads have a flat part that protrudes beyond the depression, within the projected boundaries of the sealing resin as seen from above. By doing this, the flat parts formed on the lower surfaces of the first and second external leads serve as the contact surfaces with the circuit board, these contact surface being inside the region projected from above the sealing resin, so that it is possible to shorten the parts of the first and second external leads that are exposed from the sealing resin, thereby enabling a reduction in the mounting surface area, and contributing to the reduction in size of the electronic equipment.
In the second aspect of the present invention, it is preferable that the bottom surface of the sealing resin be higher than the lowermost surface of the part of the first and second external leads that extend outside by 0.001 to 0.02 mm. By doing this, it is possible to achieve a good balance between the above-noted effect of the depression and a reduction in the size of the electronic component.